Sir,-I think Mr. Gray is hardly fair to the theory of the water-cement ratio. Professor
Abrams only tries to deal with one variable at a time; and his statement is that, other
from remaining unaltered, the lower the water-cement ratio, the higher the strengthas
long as the mixture remains workable. He stresses the qualification, to which he attributes the downward droop of the curve at low ratios. The qualification has had results of practical value in leading to the development of vibrating machines.